JPH05335327A - Heterojunction bipolar transistor - Google Patents

Abstract

PURPOSE:To provide an npn heterojunction bipolar transistor composed chiefly of III-V compound with less interstitial atoms and atomic holes. CONSTITUTION:A collector layer 3 of n<->-GaAa doped with Se which is to occupy a V group site and become a donor is formed on a GaAs substrate 1 with a buffer layer 2 in between. On top of that, a base layer 4 of p<+>-AlGaSa doped with C, an emitter layer 5 of n<->-AlGaSa doped with Se and a cap layer 6 of n<+>-AlGaAs are formed. Further, a collector electrode 7, a base electrode 8 and an emitter electrode 9 are formed, an npn heterojunction bipolar transistor composed chiefly of III-V thus formed. In this manner, difusion of impurities in each layer, i.e., the collector layer 3, base layer 4 and emitter layer 5, is suppressed and lattice defects are significantly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high speed heterojunction bipolar transistor used in the fields of microwave and high speed communication.

[0002]

2. Description of the Related Art AlGaAs / GaAs HBTs are known as conventional high-speed semiconductor devices. As a component of impurities in the conventional technique, “high-concentration doping of semiconductor and its physical properties p.
6 ”(July 5, 1991, Japan Society of Applied Physics, Applied Electronic Physics Subcommittee), the n-type layer contains IV group S
Group II Be, Zn, Mg, or the like is generally used for the n-type and p-type layers.

[0003]

When a group III-V semiconductor is doped with an impurity mainly occupying a group III site, that is, an impurity mainly substituting a group III atom, this impurity becomes a donor. At this time, many defects are caused by atomic vacancies, and conversely, when they serve as acceptors, many defects are introduced by interstitial atoms. Also, mainly V
When doped with impurities that occupy the group site,
When these impurities serve as donors, many defects are caused by interstitial atoms, and conversely, when they act as acceptors, many defects due to atomic vacancies are introduced. As a result, the mobility of the carrier in the semiconductor decreases and the diffusion of impurities in the high-concentration layer increases, resulting in a significant decrease in reliability of the device.

Specifically, in a conventional GaAs-based HBT, when Be used for the base is doped at a high concentration, Be diffuses only by passing a current.
This is "High concentration doping in semiconductors and their physical properties p.
36 ”(July 5, 1991, Japan Society of Applied Physics, Applied Electronic Physics Subcommittee).

In addition, "J. Appl. Phys., Vo
l. 67, No. 10, 15 May 1990 p.
6153 ”does not completely recover the lattice defects of GaAs due to the ion implantation, but only by annealing.
It is shown that the a-site atomic vacancies (V _Ga ) remain.

As a measure for preventing diffusion of impurities in the base layer, it has been proposed to use C (carbon) as an impurity used in the base layer. According to this, although it is possible to suppress the diffusion of impurities in the base layer to some extent, it has no effect on the diffusion of impurities in the n-type layer, and
It is not possible to reduce lattice defects.

In view of the above problems, the present invention suppresses the diffusion of doped impurities and has few lattice defects II
An object is to provide an npn-type heterojunction bipolar transistor whose main component is an IV compound.

[0008]

In order to solve the above problems, the present invention provides an npn containing a III-V group compound as a main component.
Type heterojunction bipolar transistor is formed by epitaxially growing a semiconductor layer doped with impurities mainly occupying V group sites and serving as donors, that is, impurities mainly displacing III group atoms to serve as donors. It is characterized by having an n-type emitter layer and a collector layer, and a p-type base layer formed by epitaxially growing a semiconductor layer mainly occupying a group V site and doped with an impurity serving as an acceptor. Further, the impurity serving as the donor may be Se, and the impurity serving as the acceptor may be C.

[0009]

The impurities that occupy the V group sites and serve as donors form interstitial atoms of the V group atoms, and the impurities that serve as acceptors form atomic vacancies of the V group atoms. That is, according to the present invention, the base layer is doped with an impurity serving as an acceptor occupying a group V site to form an atomic vacancy of the group V site, and the emitter layer and the collector layer occupy the group V site to serve as a donor. The interstitial atoms of the group V atoms are formed by doping these impurities.

Therefore, the atomic vacancies at the V group site in the base layer and the interstitial atoms of the V group atoms in the emitter layer and the collector layer disappear from each other.

[0011]

1 is a sectional view of an npn type heterojunction bipolar transistor according to an embodiment of the present invention.

On a GaAs substrate 1, an n ⁻ -GaAs collector layer 3 occupying a V group site and serving as a donor is formed via a buffer layer 2.
A C ⁺ -doped p ⁺ -AlGaAs base layer 4 occupying the same V group site as Se and serving as an acceptor is formed thereon. Further thereon, a Se-doped n ^-- AlGaAs emitter layer 5 and n
A cap layer 6 of ⁺ -AlGaAs is formed. Furthermore, collector electrode 7, base electrode 8, emitter electrode 9
To form an npn-type heterojunction bipolar transistor containing a III-V group compound as a main component.

Interstitial atoms 11 are introduced into the collector layer 3 and the emitter layer 5 by Se doping, and atomic vacancies 10 are introduced into the base layer 4 by C doping. The atoms 11 have disappeared from each other due to the annealing. As a result, diffusion of impurities in each of the collector layer 3, the base layer 4, and the emitter layer 5 is suppressed, and a device with significantly reduced lattice defects can be obtained.

The mechanism for preventing the diffusion will be described below.

It is generally known that the impurities occupying the V group site are less likely to diffuse than the impurities occupying the III group site. Further, it is known that the cause of diffusion of Be and Zn is a kick-out phenomenon in which interstitial Ga atoms (I _Ga ) existing in supersaturation repel Be and Zn contained in Ga sites and enter there. Has been. This phenomenon is described in “J. Appl. Phys., Vol. 69, N.
o. 6, 15 March 1991 p. 3547 "
(1991 American Institute
Of Physics). Also, Si
It is considered that the diffusion of etc. is due to the effect of atomic vacancies. These are the cases of impurities occupying the group III site,
Similarly, regarding the impurities occupying the V group site, it is considered that the diffusion of the doped impurities is strongly influenced by interstitial atoms and atomic vacancies.

Therefore, doping impurities occupying the same V group site and eliminating these interstitial atoms and atomic vacancies to reduce them leads to the effect of suppressing the diffusion of the doped impurities. Moreover, by eliminating interstitial atoms and atomic vacancies from each other, overall lattice defects are reduced, and the electrical stability of the device is improved.

The manufacturing method of the embodiment of the present invention will be described below with reference to FIGS.

Semi-insulating GaAs substrate 1 (FIG. 2 (a))
Then, n ⁺ -GaAs is epitaxially grown as the buffer layer 2, and n ⁻ -GaAs doped with Se is epitaxially grown as the collector layer 3 thereon (FIG. 2B). Due to Se doping, interstitial atoms 11 of group V atoms are introduced into the collector layer 3.

Further, as the base layer 4 on the collector layer 3, C occupying the same V group site as Se of the collector layer 3 is formed.
A p ⁺ -Al _x Ga ₁ -x As layer doped with is epitaxially grown (FIG. 2C). This base layer 4
Is a grating layer having an Al content X of 0 on the collector layer 3 side and 0.1 on the emitter layer 5 side. Also, C
By the above doping, atomic vacancies 10 of V group sites are introduced into the base layer 4.

Se is formed on the base layer 4 as the emitter layer 5.
Epitaxially grows n ⁻ -Al _X Ga _1-X As doped with. The emitter layer 5 is a grating layer formed with an Al content X of 0.1 on the base layer 4 side and 0.3 on the cap layer 6 side. It is known that Se doped here has few DX center defects. ("J. Appl. Phys., Vol. 68, N.
o. 7, 1 October 1990 p. 334
3 ”). Due to this Se doping, the interstitial atoms 11 of the group V atoms are introduced into the emitter layer as well. Further, the cap layer 6 is formed of InGaAs (FIG. 3D).

Thereafter, using a lamp annealing furnace, 800
Annealing is performed at a temperature of ˜1100 ° C. for about 0.5 to 10 seconds (FIG. 3E). By this annealing, the base layer 4
The atomic vacancies 10 and the interstitial atoms 11 of the collector layer 3 and the emitter layer 5 can be eliminated from each other.

Each layer is etched by the wet etching method, and then the collector electrode 7, the base electrode 8 and the emitter electrode 9 are formed on each of the buffer layer 2, the base layer 4 and the cap layer 6 (FIG. 1). The isolation and passivation film is coated (not shown).

The present invention is not limited to the above-described embodiment, but various modifications can be made.

Further, the impurity for doping the n layer is Se.
However, the impurity of the base layer 4 may be Si, Ge or the like of the IV group element.

[0025]

As described above, by doping the base layer with the impurity that occupies the V group site and serves as an acceptor, V
V atoms in the base layer are formed by forming interatomic vacancies of group V atoms by forming atomic vacancies at group sites and doping the emitter layer and collector layer with impurities that occupy the group V sites and serve as donors. The atomic vacancies of the group site and the interstitial atoms of the group V atoms of the emitter layer and the collector layer can be eliminated from each other.

Since atomic vacancies and interstitial atoms promote diffusion of the doped impurities, reducing the number of these lattice defects suppresses the diffusion of impurities.
That is, it is possible to suppress the diffusion of impurities into or from the base layer, which is the main cause of the problem in the reliability of the npn-type heterojunction bipolar transistor whose main component is a III-V compound. ..

According to the present invention, lattice defects in the high-concentration layer can be reduced, diffusion of impurities can be suppressed, and carrier mobility can be improved, so that the performance and reliability of the device can be significantly improved. N containing a group V compound as a main component
A pn type heterojunction bipolar transistor can be provided.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a heterojunction bipolar transistor of an embodiment of the present invention.

FIG. 2 is a schematic process diagram of an example of the present invention.

FIG. 3 is a schematic process diagram of an example of the present invention.

[Explanation of symbols]

1 ... GaAs substrate, 2 ... buffer layer, 3 ... collector layer,
4 ... Base layer, 5 ... Emitter layer, 6 ... Cap layer, 7 ...
Collector electrode, 8 ... base electrode, 9 ... emitter electrode, 1
0 ... atomic vacancies, 11 ... interstitial atoms.

Claims (2)

[Claims] 1. An np containing a III-V group compound as a main component.
In an n-type heterojunction bipolar transistor, an n-type emitter layer and a collector layer mainly formed by epitaxially growing a semiconductor layer doped with an impurity serving as a donor and occupying a group V site, and a group V site mainly And a p-type base layer formed by epitaxially growing a semiconductor layer that is doped with impurities serving as acceptors. 2. The heterojunction bipolar transistor according to claim 1, wherein the impurity serving as the donor is Se, and the impurity serving as the acceptor is C.